What this question drives at is the source of our morality and ethics.  If we intend to say that one thing is good and that the opposite is evil (and everyone must do this), then we need to be clear as to why one thing is good and the opposite is evil.  We need to be clear about our basis for morality.  For Christians, our moral basis is the revelation of our nature as broken creations of a good Creator.  Without an external, objective source for our morality, we are forced to admit that morality is something we create, and as such, it is subject to change.  If theft is wrong only because we say it is, what is to save us from changing our mind?  What provides any concrete context for defending one behavior or fighting to stop another?  Logically, nothing does.  If right and wrong are things we have defined for ourselves, then we are logically able to redefine them.  

In this case, it's the issue of global warming that has caused this philosopher to reevaluate part of his intellectual and moral construct of the world.  He recognizes that without an objective moral standard, his philosophical position is in conflict with logic and reason, and he ends up making an unfounded assertion about a given behavior.  This is the sort of intellectual honesty that more people (Christians and non-Christians!) should aspire to!  While he certainly isn't affirming that God must exist, admitting the reality of objective moral standards is definitely a huge step closer to that position - since you immediately have to answer how those objective moral standards appeared and where they came from.